Arc gap



June 17 19.24.

C. E. BENNETT ARC GAP Filed April 1,

awuntoz Patented June 17, 1924.

UNITED STATES 1,498,420 PATENT OFFICE.

CHARLES E. BENNETT, 0F DECATUR, GEORGIA, ASSIGNOR TO BALT MANUFACTURING COMPANY, OF ATLANTA, GEORGIA, A CORPORATION OF GEORGIA ARC GAR.

Application filed April 1, 1921. Serial No. 457,638.

To all w/wm it may concern:

Be it known that 1, CHARLES E. BENNETT, a citizen of the United States of America, residing at Decatur, in the county of De Kalb and State of Georgia, have invented certain new and useful Improvements in Are Gaps, of which the following is a specification.

My invention relates to are gaps, and particularly to improved gap terminals.

As pointed out in my eopending application Serial N 0. 402,569, filed August 10, 1920, patented January 1, 1924, No. 1,479,693, of which the present application is in part a continuation, large and small gap terminals present different phenomena on are formation. Between needle terminals, or approximations thereto, corona phenomena occur preceding an actual arc-over. This delays the discharge across the gap. On the other hand, between large terminals, such as sphere terminals, the arc-over is immediate without preliminary corona formation. There is consequently no delay in the discharge across the gap.

It is also a recognized fact that sphere terminals of larger size may be spaced closer together than like terminals of smaller size at the same gap resistance or rating.

In protective ground connections for high voltage lines, it is desirable to provide gap terminals which, although exposed to the elements, will operate with practical uniformity under dry and wet weather conditions. The presence of moisture, such as heavy fog or rain, however, materially lowers the gap resistance, thus ordinarily necessitating a greater spacing between the exposed terminals than is desirable, since this additional spacing between the termi nals renders the gap less sensitive to surges under dry weather conditions.

Among the greatest dangers to equipment on power-line installations, are high fre-,

quency currents; that is to say currents characterized by steep wave front. Unless such a current is discharged at once before it reaches equipment, such as transformers, the latter are likely to be burned out and ren dered useless. These currents'may be im-- posed upon the line at any time, either under wet or dry conditions.

The object of the present invention is to provide gap terminals of a construction such that they discharge with substantial uniformity under wet and dry conditions at the gap, whether the dangerous current imposed upon the line is of either high or low frequency. While the construction shown combines these characteristics, they are not necessarily interdependent since the means employed to effect prompt discharge ofhighfrequency current may be utilized to advantage without reference to the means by which the lowered resistance of the gap under moisture conditions is compensated. The latter feature alone forms the subject of my earlier application, Serial No. 384,221, filed May 25, 1920 (Patent N 0. 1,479,692, January 1, 1924), and is therefore not specifically claimed herein.

In the accompanying drawings Fig. 1 is a diagram of an illustrative installation in which ga terminals of the present type may be use to advantage;

Fig. 2 is a side elevation of the terminals alone, drawn to a large scale and indicating diagrammatically the electrostatic flux field formed between the terminals by the lowfrequency current;

Fig. 3 is a similar View indicating diagrammatically the flux field between the terminals under the influence of high-frequency current;

Figs. ,4, 5 and 6 are vertical sections through terminals of various constructions in which my invention is variously embodied.

The installation shown in Fig. 1 represents a power line 10 having a ground connection 11, in which is arranged a gap 12 and an ar-.

rester 13 of any suitable sort for breaking the ground connection 14 after the excessive current has been drained from the line. The terminals of the gap 12 are illustrated on a larger scale in Figs. 2 and 3. As here shown, each terminal comprises a metallic button 15 (preferably a segment of a sphere) directly connected to the ground line. Surrounding the button is a disk 16 of insulation, preferably ofmois'ture-absorbent material, such as lava, porous porcelain, or other suitable buttons is such, however, that on a surge. at line frequency the arc-over may be preceded by slight corona formation with resultant lag in the discharge. This occasions no danger to equipment so long as the surge isof low frequency since the duration of the corona phenomenon is not long enough to permit the surge current-to reach the protected equipment before the are forms and the line is drained to ground.

- When a high-frequency current, however,

is imposed upon the line, such a corona lag in the formation of the arc is dangerous to .the equipment. A high-speed discharge is essential to the effectiveness of the p'rotec tive ground line. Such high-speed discharge is attained by the present invention. In the terminals of'Figs. 2 and 3, it results from the presence of the metallic ring 17 surrounding the button 15, especially when combined with the associated metal plate .18. Effective results are secured without the plate 18,as pointed out in my application Serial No. 402,569, now Patent No. 1,47 9,- 693,, but I have found that the plate materially accentuates the condenser action of I the ring 17, and I therefore prefer to combine thetwo in the manner indicated, for best results.- The effect of the ring 17 under the influence ofhigh-frequency current is to greatly enlarge the electrostatic flux field between the terminals. Under the influence of low-frequency surges the fieldis.

practically restricted to a limited area 19, iagrammatically indicated in Fig. 2. Under the influence of'high-frequency currents, the condenser action of the rin greatly expands this field, dia ammatica yindic'ated M20 in Fig. 3.. e plate 18 accentuates th scondenser action, the lines of force bemg indlcated diagrammatically at 21. With th s greatly enlarged and uniform flux field there is no corona formation, and no lag in the arc-over." The high-frequency current is therefore discharged with high speed across the gap, without hesitation or possibility of the current reaching the protected equipment. r I

I have found, furthermore, that the effectof the plate 18 upon the flux field 20 between the terminals, varies with the spacing of the plate from the ring 17. Thus,

by arranging the plate closer to the ri its efiect appears to e to expand the fiel 20 and to render the distribution of the lines of force more uniform,as indicated in Fig.

3; whereas by moving the plate further.

" the condenser ring 17.

away from the ring the flux field is not so gap to the line. This is particularly desirable from a practical standpoint, since the terminal construction may be made standard (within certain limits), and the speed of the gap regulated by the adjustment of the plate toward or from the ring. The means for securing the plate in adjusted position may be of any suitable character fo"r example, a set screw X passing through the hub Y of the late and engaging the rod 11.

l! hile I have shown .my preferred construction in Figs. 2 and 3, the same idea in different forms is embodied in the remaining figures. Thus in Fig. 4, I have shown the rings 17 of the two terminals associated with condensers 22 of any suitable type.

In Fig. 5 the condenser action is secured not'by an independent disk, as in Figs. 2 and 3, but by a back plate 23 integral with The back plate may be further continued by a sleeve 24 surrounding the line 11 and spaced therefrom by an insulating bushing 25.

In Fig. 6 I have substituted for the sleeve 1 24 a second back plate 23 connected to the line but. spacedfrom the plate 23 by an interposed di-electric 26 of any suitable sort. In this figure I have indicated diagrammatically a connector clamp 27, which would be utilized in some form or other in all of the constructions to electrically connect the ground lead 11 to the gap terminal. At the terminal the ground line may take the form of a rod of sufiicient mechanical strength, not only to support the disk 16, ring 17, and-plate 18, but also to afford the means by which the terminal is supported upon an associated insulator, bracket, or the like (not shown).

Itis of course obvious that this automatic acceleration of the gap is due to the nature of the current imposed on the line-that is to say high-frequency surgesand is in no way dependent upon alteration of physical conditions, as e. g., the presence of moisture at the gap.

As above mentioned, the spacing between gap terminals has ordinarily been adjusted with relation to the reduced resistance at the gap due to moisture conditions. By making the di-electric disk 15 of porous or moisture- .absorbent insulating material, it is possible to make the gap spacing of the buttons 15 suitable for dry weather conditions, that is to saymuch closer, than would be safe. in

the presence of moisture at the gap. Upon the wettmg of the di-electric 16 by moisture isfre at the gap, it becomes a conductor and has the effect of enlargin the terminal area to the full diameter of the ring 17. As is well known, the tendency to arc-over between large spheres is less than that between small spheres at the same setting. Consequent- 1%, the enlarged terminal area afforded by t e wetted disk 16 compensates the lowered resistance at the gap by enlar ing the conductive area of the terminals. e flux field under moisture conditions at the gap is substantially that-indicated in the area 20 in Fi 3, the lines of flux at 21 being absentun ess the execessive current be one of high uency.

e terminal thus combines protection of the gap against lowered resistance under moisture conditions by automatically enlarging the terminal area, with automatic elimination of corona lag under dry weather conditions when subjected to high-frequency impulses. Of course the high-frequency impulses pass the gap without hesitation under moisture conditions, since corona lag is already eliminated b the enlarged terminal area afforded by the wetted disk 16.

The constructions illustrated are merely examples which embody my invention in practical form and are subject to various modificationswithout departing from what I claim as my invention.

I claim- 1. An arc gap terminal comprisin a conductor connected to the line, a meta ic ring surroundln but spaced from said conductor, and adjusta le means for increasing the condenser efiect of said ring.

2. An arc gap terminal'comprisin a conductor connected to the line, a meta ic ring surroundin and a meta lic element connected to the line and spaced from said ring to increase the condenser effect thereof.

3. An arc gap terminal comprisin a conductor connected to the line, a meta 'c ring surrounding but spaced from said conductor, and an adjustable metallic plate spaced from said ring to increase the condenser efiect thereof.

4. An arc gap terminal comprisin a conductor connected to the line, a meta ic ring surrounding but s a'ced from said conductor, and a metallic p ate connected to the line but spaced from said ring to increase the condenser effect thereof.

5. An arc gap terminal comprising a conbut spaced from said conductor,

- said ring.

7. An arc gap terminal comprising a ter- 'minal conductor connected to the line, a

moisture absorbent insulator associated with said terminal conductor and serving to increase the effective conductor area of the terminal under moisture conditions at the gap, a metallic rin associated with said insulator and space thereby from the terminal conductor, and means for varying the condenser action of said ring.

8. An-arc gap installation comprising a pair of spaced gap terminals in combination with a pair of condenser plates arran ed respectively back of the gap terminals ut movable toward and from the latter to adi'xust the break-down rating of the gap for igh frequency current.

9 An arc gap installation comprising a pair of spaced gap terminal conductors, porous insulation associated with said terminal conductors and servin to increase the effective conductor area of the terminals under moisture conditions at the gap, together with condenser elements associated with the terminals, and means for varying the condenser effect of said condenser elements to vary the break-down rating of the gap for high frequency current.

10. An arc gap installation comprising a pair of spaced gap terminal conductors, porous insulation associated with said terminal conductors and serving to increase the 100 efiective conductor area 0 the terminals under moisture conditions at the gap, a metallic member surrounding said lnsulation and spaced thereby from the terminal conductor, together with condenser elements 1 associated with the terminals, and means for varying the condenser efiect of saidcondenser elements to vary the break-down rating of the gap for high frequency current.

In testimony name to this's ecification.

HARLES E. BENNETT.

whereof I have signed my 1 

